In the power generation and distribution industry, utility companies generate electricity and distribute the electricity to customers. To facilitate the process of distributing electricity, various types of power switching devices are used. In a distribution circuit, electricity flows through the power switching devices from a power generation source (typically a substation or the like) to the consumer. When a fault is detected in the distribution circuit, the power switching device is opened and the electrical connection is broken.
Controllers are used by the utility company to detect faults that occur in the distribution circuit. This type of controller typically uses a microprocessor programmed to respond to the fault based on the type of fault and the type of power switching device connected to the controller. The controller may respond to a particular fault by causing the power switching device to remain open. Alternatively, upon the detection of a fault, the controller may cause the power switching device to open and close multiple times.
In order to determine if a fault is present in the distribution circuit, the controller monitors the amount of electrical current flowing through the power switching device. If the amount of current exceeds a preprogrammed threshold for a certain period of time, the controller instructs the power switching device to perform the preprogrammed response.
Within the power switching device, a current transformer is generally used to monitor the current levels. The analog signal from the current transformer is sent to the controller and the controller processes the analog signal. In previous controller designs, an “auto-ranging” current detection scheme is implemented. In order to auto-range, the controller contains hardware and software that allows it to be able to determine the range of current being conducted. Once the range is determined, a specific value is then established by the controller. This type of auto-ranging circuit generally uses a single current measurement circuit.
One drawback to the auto-ranging controller is that the accuracy of current measurement diminishes as the current values get smaller. The controller needs to accurately measure current levels in the range of 20 amperes up to 24,000 amperes. The present invention provides an accurate measurement of current flowing through a power switching device and improves the accuracy of the current measurement at a cost lower than the current measurement of the auto-ranging scheme.